This invention relates to a speed reducer, more particularly, to a speed reducer which employs a variety of rolling means. Accordingly, conventional speed reducers which employs the differential gear transmission, such as planetary gear speed reducer, cyclo drive speed reducer and gear pin drive speed reducer, are generally distinguished from their transmission means which are respectively planetary gear 2, cycloid disc 4 and sliding gear pin 8. (See FIGS. 1 to 3)
Referring to FIGS. 1A and B, a planetary gear speed reducer includes a planetary gear 2 which is driven by a crank shaft 3 and restricted within an internal gear 1. In accordance with the transmission principle of the planetary gear, the angular velocity is W2/W1=-1/P. The P is the remainder given by subtracting the teeth of the planetary gear 2 from the teeth of the internal gear 1. The highest ratio of the speed reduction may be obtained by the counter-rotation of the planetary gear 2. However, the tooth interference may be caused by the limit of gear profile on isolute between the planetary gear 2 and the internal gear 1. Additionally, the cost of the planetary gear speed reducer is raised by its complicate manufacturing process.
FIGS. 2A and B show a cyclo drive speed reducer including a cycloid disc 4 driven by an eccentric rod 7 and restricted by a plurality of ring gear pins 5. In accordance with the principle of the differential gear transmission, the cycloid disc 4 revolves around the ring gear pins 5 and rotates on the eccentric rod 7. Since the ring gear pins 5 are smoothly circular in shape and the cycloid disc 4 rotates in a cycloidal oscillation, the contact between the cycloid disc 4 and the ring gear pins 5 therefore reduces to improve the differential gear mechanism which gear difference may be ranged from one to four teeth. However, the manufacturing cost is raised due to the complicated structure of the cyclo drive speed reducer.
FIGS. 3A and B show a gear pin drive speed reducer comprising a plurality of sliding gear pins 8 which are driven by an eccentric rod 7, engaged with a plurality of ring gear pins 5 and restricted within a slow speed shaft disc 10. The slow speed shaft disc 10 directly causes the speed reduction. The disadvantages of the gear pin drive speed reducer are enumerated hereinafter. First, when the slow speed shaft disc 10 braked by the sliding gear pins 8 while in their rotation suddenly, due to the centrifugal force and the gravity, the sliding gear pins 8 may easily disengage from the slow speed shaft disc 10 to cause the jamming of the operation. Even though the disengagement of the sliding gear pins 8 from the slow speed shaft disc 10 does not occur, the gear pin drive speed reducer will make a loud noise by its violent shaking because of the unstable rotating speed of the sliding gear pins 8. Furthermore, the temperature of the gear pin speed reducer apparently rises during its longtime operation.